1. Field of the Invention
Embodiments of the present invention relate to printers and, more particularly, to printers including platens that incorporate electromagnetic couplers for coupling to radio frequency identification transponders.
2. Background Information
Radio frequency identification (RFID) transponders or tags, either active or passive, are typically used with an RFID interrogator or similar device for communicating information back and forth. In operation, the interrogator exposes the transponder to a radio frequency (RF) electromagnetic field or signal. In the case of a passive ultrahigh frequency (UHF) transponder, the RF electromagnetic field energizes the transponder and thereby prompts the transponder to respond to the transceiver by re-radiating the received signal back and modulating the field in a well-known technique called “backscattering.” In the case of a passive high frequency (HF) transponder, the transponder modulates the impedance of an antenna to which it is magnetically coupled in order to send data back to an interrogator. In the case of an active transponder, the transponder may respond to the electromagnetic field by transmitting an independently generated and powered reply signal to the transceiver.
Problems can occur when interrogating multiple adjacent transponders, regardless of whether the transponders are powered by an on-board direct current (DC) power supply or by a RF field generated by a separate RFID interrogator. For example, an interrogating electromagnetic signal may activate more than one transponder at a given time. This simultaneous activation of multiple transponders may lead to communication (i.e., read and write) errors because each of the multiple transponders may attempt communication with the transceiver at the same time. Such communication interferences are known as “collisions.”
Several collision management techniques commercially exist for allowing near simultaneous communication of a single interrogator with multiple transponders while reducing communication errors. However, such collision management techniques tend to increase system complexity and cost, and may also result in delayed response. Furthermore, such techniques are often “blind” in that they cannot locate a given transponder or more specifically recognize the position of a transponder within the interrogating RF electromagnetic field.
Another method of preventing the activation of multiple transponders is to electromagnetically isolate transponders from one another. For example, devices or systems may employ an RF-shielded housing or anechoic chamber for shielding the adjacent and non-targeted transponders from the electromagnetic field. In various applications, transponders individually pass though a shielded housing for individualized exposure to an interrogating RF electromagnetic field. Unfortunately, RF-shielded housings add cost and complexity to a system and limit the type (e.g., size) of transponders that can be processed by the system. Furthermore, many systems in which RFID tag interrogation might be employed are limited with regard to space or weight and, thus, cannot accommodate such shielded housings.
The challenge of avoiding multiple transponder activation may be especially acute in the case of RFID printer-encoders. RFID printer-encoders are devices capable of encoding and printing on a series or stream of labels having respective embedded transponders. The close proximity of the transponders to each other during processing makes targeting a particular transponder for encoding purposes problematic. Moreover, the space, cost, and weight restrictions associated with such devices, among other factors, make collision management techniques or shielding components for alleviating multiple transponder activation less than desirable. Further, “blind” collisions management techniques could lead to uncorrelated printing and data encoding for a given RF label.
In light of the foregoing it would be desirable to provide a RFID system or device capable of interrogating individual transponders positioned among multiple adjacent transponders without the need for collision management techniques or shielding components. It would be further desirable for such a RFID system to designate, with some degree of certainty, a specific transponder to be interrogated among multiple adjacent transponders, and to be capable of encoding a transponder positioned at or very close to a printline.